UKH

Hi,

I'm thinking about buying an oversized, fairly lightweight synthetic bag that will fit over a 2 season down bag without squashing its loft. Has anyone discovered any (cheap-ish) options that work well?  The PHD one is way beyond my budget.

I used to use a cheapish Haglof one which was quite broad and fitted my ME down bag well inside. But I must have bought it 15 years ago so not much help I'm afraid. I guess going to Decathlon or Go Outdoors and just looking at how different models vary in shape would be your best bet.

If you can find a suitable bag, I suspect you'll find the system works rather well. My old ME bag was rated to I think -7 and by putting the basic Haglof bag over it, I could keep warm down into the low negative teens. Particularly when car camping, it got me through a good few Finnish winters.

If you move with the bag rather than within it you might consider a mummy fibre pile bag inside. This shouldn't compress a differentially cut down bag outside it and a simple one might be easy to make if nothing commercial was available.
Failing that it might be possible to use a synthetic sale price kid's bag, from Millet's etc, as an inner; possibly joining up parts of two so you had both length and a hood. Apologies for not answering the original question and I have no practical experience of this.

I've toyed with making one from thinsulate and pertex.

e.g. https://www.profabrics.co.uk/products/thinsulate-cs150-insulated-wadding

Would be quite an easy project if you've any experience of sewing,

I use a really cheap decathlon jobbie, has served me well outside my big down bag on several trips to Alaska. 

Shit, this beer is strong!

i’ve got A mammut kompkakt one season bag that fits over a down bag well. Really most cheap one season bags do the job as generally have a loose cut. I’d worry some of the lighter synthetic bags that offer high performance would be a bit tight.

On a hunt for something else I saw a Snugpak 'The Sleeping Bag'. which looked like it might be a looser fit, and not too over spec'd bag.  At under £30.  I thought of this thread.

I used to have a Snugpak synthetic bag and it was well made.

Thanks a lot for all the suggestions. I've just settled on a squared- off, "envelope" style cheapie from Highlander, mainly because the filling rejoices in the title "7 hole Qualofill", albeit only 100 g.s.m. (!)

I'll let you know how I get on.

Cheers.